Privacy policy of the “RudelKey” app

Last updated: 24 October 2026 · applies to the Android app RudelKey (de.christiankempf.rudelkey), the RudelKey Windows program and the “RudelKey for Firefox” extension. The website is covered by the general privacy policy. In case of doubt the German version prevails.

In short: your passwords are stored encrypted on your device. If you turn on sync, they go encrypted into your own cloud folder. Without your master password or your emergency kit nobody can read them – not even me. There is no account, no server and no advertising.

1. Controller

2. The vault on your device

All entries – title, website, username, password, 2FA key, notes and the history of earlier passwords – are stored in the app’s storage, each encrypted individually (XChaCha20-Poly1305). RudelKey derives the key from your master password (Argon2id). The master password itself is not stored and never leaves the device. The recovery key from the emergency kit is only shown during setup and is not transmitted either. RudelKey locks itself again after the time you set.

3. Autofill on the phone

If you enable RudelKey as autofill service, Android passes the structure of login forms in other apps and in the browser to the app (field types, name of the app or address of the page). RudelKey only uses this to suggest matching entries and to save new logins. This information does not leave the device; only what you explicitly save is stored, and which entry you chose for an app.

4. Firefox extension on Windows

The “RudelKey for Firefox” extension detects login fields on web pages and shows matching logins for them. It only talks to the RudelKey program on the same PC: via Firefox’s native messaging interface to a small intermediary and from there exclusively to 127.0.0.1. What is transmitted is the address of the page and – if you want to save a login – what you typed on the page. If the vault is locked, the program releases nothing. The extension collects no data and sends nothing to the internet.

5. Fingerprint and Windows Hello

Unlocking by fingerprint is handled by Android, on Windows by Windows Hello (PIN, face or fingerprint). RudelKey receives no biometric data, only the result; the key for it is stored in the Android Keystore or in Windows’ key management.

6. Clipboard

RudelKey clears copied passwords, usernames and 2FA codes from the clipboard again after 30 seconds. On Android they are marked as sensitive so they do not appear in previews; on Windows they are kept out of the clipboard history and the clipboard’s cloud sync.

7. Sync via your cloud folder (optional)

If you turn on sync on the phone, RudelKey stores the encrypted vault in a folder “RudelKey” in your OneDrive. You sign in with your Microsoft account (login.microsoftonline.com); the files run via the Microsoft Graph interface (graph.microsoft.com). The provider is Microsoft Ireland Operations Limited, One Microsoft Place, South County Business Park, Leopardstown, Dublin 18, Ireland; Microsoft’s privacy statement applies. On Windows RudelKey writes to a folder on the PC that you choose; your sync program (such as OneDrive, Nextcloud, Dropbox or Google Drive) takes it to the cloud, and its provider is responsible for that.

Only encrypted data goes into the folder. The provider sees no passwords or entries, only encrypted files and the technical details that come with any storage (account, file size, time, IP address). The sign-in tokens are stored encrypted in the Android Keystore. The legal basis is Art. 6(1)(b) GDPR. Without sync RudelKey makes no connection to the internet.

8. Family and shared vaults (optional)

If you found a family, RudelKey creates a folder “RudelKey Familie” in your OneDrive, which you share with the others. It holds the shared vaults, each with its own key, and the member list with names, role (parent or child) and the devices’ public keys – all signed and, where it concerns content, encrypted. Only those confirmed by a parent after comparing a check code are admitted. If you use recovery via the family, each chosen helper receives an encrypted part of your key; a single part reveals nothing. The legal basis is Art. 6(1)(b) GDPR.

9. Import

When importing, RudelKey reads the CSV file you pick via the file picker and encrypts the entries. The file itself stays where it is – delete it afterwards, as it contains all passwords unencrypted.

10. Permissions (Android)

11. No advertising, no analytics

RudelKey contains no advertising, no analytics tools, no trackers and no crash reporting.

12. Retention and deletion

The data stays on your device until you delete it in the app or uninstall the app. You delete the folder in the cloud there yourself. Android may include app data in your personal device backup if you have enabled this in the system settings; the vault stays encrypted there.

13. Your rights

As I receive no data from the app and cannot decrypt the vault, I cannot provide information about it or delete it; you are in control – on your device and in your cloud folder. For questions, contact me at the address above. You may also lodge a complaint with a data protection supervisory authority, for example the one responsible for me: the State Commissioner for Data Protection and Freedom of Information Baden-Württemberg, Lautenschlagerstraße 20, 70173 Stuttgart, Germany.